To determine the potential value of electrical impedance myography (EIM) for assessing lower back muscle condition in low back pain (LBP) patients.

The condition of lower back muscles is thought to be an important factor in LBP. Yet methods for quantifying their status are limited. EIM could offer a simple approach for quantifying lower back muscle health.

A group of patients with chronic LBP with mixed etiologies and a group of healthy subjects were recruited and measured with the mView EIM device (Myolex, Inc). Paraspinal muscles on both sides of the lower back were measured at the L4-5 levels using a 4-electrode array placed directly over the muscles. In addition to raw EIM parameters, the 100 kHz normalized difference (side-to-side difference/average of both sides) was calculated for all subjects.

A total of 86 healthy individuals  (median age (interquartile range) (IQR), 45.5 years (30.3-56.0 years), 42 men, 44 women) and 47 low back pain patients (median age 51.0 year (39.5-57.5) years, 21 men, 26 women) were enrolled.  Median EIM 100kHz phase was lower in the LBP patients (9.3°(IQR8.4°-10.6°) versus 11.4°(IQR 9.4°-13.0°), p=0.0007).  Significantly increased normalized side-to-side differences were present for all three EIM variables (e.g., median 100 kHz phase 0.15 (IQR 0.07-0.31 in LBP patients versus 0.09 (IQR 0.04-0.17) in healthy individuals).  A significant correlation between 100 kHz EIM phase and reactance was found with age (R_Spearman=-0.46, P=0.0002 and R_Spearman=-0.44, P=0.0003) but not for resistance.

We have identified reductions in EIM phase values in patients with LBP as compared to a healthy population and greater asymmetries in EIM values for phase, resistance, and reactance. An age dependency in these values was also identified. Overall, these data support that EIM has the potential to serve as a useful tool for assessing muscle condition in LBP patients.